1. Field of the Invention
The present invention is directed generally to data switching systems and more specifically to a method for accessing address features of communication subscribers having a first address area when sending dam packets.
2. Description of the Related Art
A variety of tests are implemented in communication connections, particularly upon set up and clear down thereof. These tests are particularly related to declarations between a communication subscriber and a purveyor of communication services.
For example, such features of communication connections are time-dependent use tariffs, allowable recipient addresses, allowable subscriber groups of communication connections, and receiver groups addressable in common. A constant set up and clear down of the connection particularly occurs when switching and sending data packets.
A plurality of addresses are therefore contained in the data packets of a data switching system. A switching computer, which processes a data packet, must usually check addresses for a plurality of conditions, as indicated above. Such checks are generally provided for via table accesses. Address features corresponding to the individual addresses are therefore contained in these tables.
The matching entry in the respective table must be found for a specific address. For example, the matching address for a sender address or a receiver address is necessarily searched for a longer time period when there are more such tables. The address itself thereby represents what is referred to as a search key. The entry in a table matching the respective search key generally contains the search key itself along with further information to enable a check of whether the key used for the search and that of the table entry agree, i.e. whether the correct table entry has been addressed. It is desirable that the search procedures sequence as quickly as possible, particularly when such address search processes occur frequently, as is the case of data switching computers.
An example of a known solution for addressing tables is hashing. In hashing, the search key is directly used as the argument of a hash function which, in the ideal case, directly supplies the sought memory location of the table as a result. In this case, the search key would be stored under the address. This method of hashing is generally very fast but is sometimes not fast enough, since the calculation of the hash function using software is often complicated. A corresponding plurality of hash function calculations must be implemented particularly when there are many tables, which leads to a considerable overall calculating time.
A binary search represents another known possibility for locating table entries. Given the application thereof, one reaches a defined upper limit for the search time. However, it assumes an ordered table and has problems with table updates. In general, it is not as fast as hashing but utilizes the available storage space more efficiently.
Direct addressing represents yet another known possibility for locating table entries. The key would thereby be directly used as an address in this method. Thus, this is the fastest overall software addressing method. However, a great deal of storage space is required, and the space is incompletely used. This is particularly true when only a limited, substantially smaller sub-plurality of addresses are selected from a large address area. Given a 64-bit wide CCITT E. 164 address for both the sender address as well as the receiver address, 2.sup.64 entries would be required for a table. This is true even though only 2048 addresses thereof are possibly used in a switching system. Also, given a 32-bit wide entry per theoretically possible address, this would require a memory having the size 7.2.times.10.sup.10 Gbyte, of which only 8 Kbytes would be filled.
It is an object of the present invention to provide a method for fast access onto address features of communication connections that are deposited in tables.
The method of the present invention advantageously exploits the fact that performance features associated with a customer are interrogated in a repeating sequence, and the number of these performance features is known. These features are thus deposited in a fixed plurality of tables and must constantly be re-interrogated in a repeating sequence for every data packet. The method of the invention advantageously provides a solution to this problem. First, the large, allowable address area is compressed onto a small address area having consecutive neighboring addresses. Second, the table search occurs via offsets of the addresses of the miniaturized address area. When the direct allocation is implemented via a hash function, an advantageous combination of hash-function addressing and direct addressing results. A greater speed advantage is achieved over direct addressing depending on the size of the number of tables.
Further, communication traffic for the addressing is advantageously reduced by the miniaturization of the address area. Since, for example, data words that are only 11 bits wide instead of 64 bits wide are searched, the result of the data search is obtained much faster.
Further, the method of the invention can be accelerated because it is not the addresses of the first address area that are stored in the tables but the addresses of the second address area. Thus, search actions are advantageously quicker by using the miniaturized addresses.
As inventively provided, a further speed acceleration is advantageously obtained when the presence of an address in a table is identified by 1 bit. Thus, a table search thereby only involves checking a set bit instead of checking for the presence of an address. For example, a plurality of existing addresses are thereby indicated by a bit word.
The method of the invention is particularly advantageously suited for use in communication connections in combination with the review of access authorizations. An accelerated and a reliable sequencing of data communications can be assured with the method of the present invention.
Further, data packet switchings can be accelerated by using the method of the invention, to check packet addresses and receiver addresses that are frequently required in such switchings.
The objects of the present invention are inventively in a method for accessing address features of communication subscribers area when sending data packets, having the steps of providing at least one first address corresponding to each the communication subscriber in a first address area, entering address features of the communication subscribers into an addressable memory, selecting an arbitrary subplurality of the first addresses from the first address area, prescribing a second address area having a plurality of second addresses incremented such that consecutive addresses of the memory are addressed, the plurality of second addresses corresponding to the sub-plurality of the first addresses, allocating exactly one first address to each second address, accessing a first address feature via a second address, and accessing further address features via an offset of the second address.